First question - have you done an error code check and what did it reveal? Here's the tricky situation. 1990 build trucks had a one year only production run using this particular ECU and peripherals (air sensors, tps etc) so if it goes bad you only have the option of finding one from the same year model. Next question - are you getting any signal from the distributor? The ICM in the distributor triggers both ignition and injector pulse so if it goes bad you won't get either events taking place (no fuel, no spark...)